Multiple-input, multiple-output (MIMO) schemes are being widely considered as means for increasing the channel capacity in wireless communication systems. In order to maximize the throughput of a multi-user (MU)-MIMO system, there is a need for an effective scheduling technique for selecting active users and the number of data streams for each user.
Conventionally, research on scheduling techniques in MU-MIMO systems have been mainly in association with methods of selecting active users from a plurality of users, methods of selecting the number of data streams for each user in a fixed active user group, and methods of performing scheduling in a condition where both the active user group and the number of data streams for each user are fixed. A transmitter of the system performs scheduling to achieve capacity maximization according to channel feedback information of each user. However, conventional research has drawbacks in that uplink resources are wasted since channel feedback is required for each user whenever scheduling is performed to select active users and the number of data streams for each user. In addition, computational complexity increases as a result of the scheduling.
In one conventional technique, a method based on a linear process that is easily implemented in practice is the Space Division Multiple Access (SDMA) technique. However, since an SDMA technique performs scheduling according to the channel feedback information of each user, the amount of feedback greatly increases when operating a system having a plurality of transmit (Tx) antennas. As a result, computational complexity increases in the transmitter or receiver. Therefore, it is difficult for an SDMA technique to be applied in a system having multiple Tx antennas.
Accordingly, there is a need for a scheduling technique for minimizing the amount of channel feedback of a user in a MU-MIMO system and a method of reducing a computational complexity in a transmitter or a receiver by using the scheduling technique.